Although the name Vaca Muerta Formation was introduced in 1931 by an American geologist Charles E. Weaver, the highly bituminous shales in the Salado River Valley in southern Mendoza were described in 1892 by Dr. Guillermo Bodenbender.
Main geological features
The Vaca Muerta Shale is a continuous tight oil and shale gas reservoir of late Jurassic(Tithonian) and early Cretaceous (Berriasian) age formation.
The formation covers a total area of 30,000 square kilometres.
The shale is at a depth of about 9,500 feet (2,900 m) where it has been found productive of oil and gas. Although called a shale, and with a total organic carbon content varying from 1 percent to 5 percent, the Vaca Muerta is predominantly marl and consists of mature black shales, marls and lime mudstones.
Formed in a marine environment with little clay and brittle rock the deposit is 30 to 1,200 metres (98 to 3,937 ft).
The Vaca Muerta Formation represents most distal facies of the Lower Mendoza Mesosequence, a Tithonian–Valanginian broad shallowing-upward sedimentary cycle.
In the southern part of the Neuquén Basin the Lower Mendoza Mesosequence includes the basinal deposits of the Vaca Muerta Formation (early to middle Tithonian), which to the south-southeast change to mixed carbonate-siliciclastic nearshore deposits of the Carrin Cura Formation (lower part of the middle Tithonian) and Picún Leufú Formation (middle Tithonian – lower Berriasian), and to continental deposits of the Bajada Colorada Formation of Tithonian – Berriasian age.
In the central part of the Neuquén Basin, also known as Neuquén embayment, the Lower Mendoza Mesosequence consists of basinal deposits of the Vaca Muerta Formation (early to upper Tithonian), which to the east change to shoreface deposits of the Quintuco Formation (upper Tithonian – lower Valanginian), and to sabkha deposits of the Loma Montosa Formation (lower Valanginian), forming a mixed carbonate-siliciclastic depositional system.
Westward the Vaca Muerta Formation includes slope facies (Huncal Member), and in the Chilean territory pass into shallow marine/volcanic deposits.
By contrast, in the southern Mendoza area the Lower Mendoza Mesosequence consists of aggradational and divergent sequences, with a maximum thickness of 500 m towards the center of the basin.
It includes basinal to middle carbonate ramp deposits of the Vaca Muerta Formation (early Tithonian – early Valanginian) and middle to inner ramp oyster-deposits of the Chachao Formation (early Valanginian), which form an homoclinal carbonate ramp system.
The Vaca Muerta Shale has long been known as a major petroleum source bed for other formations in the Neuquén Basin, which has had oil production since 1918. Wells producing from the Vaca Muerta itself are in several oil fields, including the Loma La Lata, Loma Lata Norte and Loma Campana fields.
Repsol-YPF recognized the productive potential of the Vaca Muerta Shale of the Neuquén Basin and completed Argentina’s first shale gas well in July 2010, at the Loma La Lata field. Then in November 2010, the company completed a tight oil well in the Vaca Muerta Shale in the Loma Campana area.
The first horizontal well in the Vaca Muerta was drilled and completed in August 2011.
By October 2012, 31 wells had been drilled and completed, and another 20 had been drilled and were waiting completion. The drilling had extended the Vaca Muerta field to an area of at least 300 square kilometers.
One problem in attracting development was Argentina’s price controls on natural gas, keeping the price down to U.S. $2.00-$2.50 per million BTU. However, the government exempted tight gas from controls, and in 2011 the Vaca Muerta gas was selling for U.S. $4–$7. The higher gas prices attracted major oil companies, including ExxonMobil, Total S.A. and Chevron Corporation, to Vaca Muerta.
In May 2013, YPF announced that it had negotiated a joint venture in which Chevron would invest U.S. $1.5 billion drilling 132 wells on the Loma Campana field.
Chevron’s participation was complicated by efforts by the plaintiffs who obtained a judgment in Ecuador with respect to actions by Texaco in the Lago Agrio oil field to collect the judgment from Chevron’s Argentine assets.
On September 24, 2013, YPF announced that Dow Chemical Company subsidiary Dow Argentina had signed an agreement to drill 16 natural gas wells in the El Orejano block of the Vaca Muerta formation over a 12-month period, with Dow contributing U.S. $120,000,000 and YPF U.S. $68,000,000.